Piezoelectric pump



July 14, 1970 E. H. CASEY PIEZOELECTRIO PUMP Filed NQV. 13, 1968 2O VOLTAGE GENERATOR.

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V 6| L Q 48 E 26 fi 30 Q I' i 111111151 11 qppnnmmmqmu Q Q 62 lg: 24 60 Q Q 46 5 i 36 \l E 42 FIG 2 INVENTOR EDWARD H. CASEY United States Patent 3,520,641 PIEZOELECTRIC PUMP Edward H. Casey, Creve Coeur, Mo., assignor to ACF Industries, Incorporated, New York, N.Y., a corporation of New Jersey Filed Nov. 13, 1968, Ser. No.'775,412 Int. Cl. F04b 19/00 U.S. Cl. 417-412 7 Claims ABSTRACT OF THE DISCLOSURE A double diaphragm pump is constructed using a piezoelectric crystal or stack of such crystals to reciprocate a pair of rigid, preferably metallic, diaphragms which are clamped about the crystal structure in such a manner that the crystal structure causes the diaphragms to move in opposing directions upon energization and de-energization by a suitable voltage source. Inlet and outlet valves are provided so that fluid can enter when the pumping chamber volume increases and be discharged when the chamber volume decreases.

BACKGROUND OF THE INVENTION Pumps actuated by piezoelectric crystals are known in the prior art. Williams in U.S. Pat. 3,194,162 discloses a fuel injector which is a piston type pump in which the piston is caused to reciprocate by the expansion and contraction of a stack of piezoelectric crystals. In another form of piezoelectric pump the piezoelectric crystal structure is actually in the form of a bending element that deforms elastically under electric stress and thus the crystal structure itself forms a diaphragm which reciprocates or bends inwardly and outwardly to provide the pumping action. This latter form of pump is exemplified by Johnson et al., U.S. Pat. 3,107,630.

It is well known that piezoelectric crystals possess the ability to expand and contract along a predetermined axis upon the electrical excitation of the crystal. It is this expansion and contraction that enables such crystals to be useful as drive means for pumps. In the case of the piston type pump the expansion is axial and thus the crystal is basically in a condition of being under compression. The degree of compression being controlled to effect the pumping action. In the case of the piezoelectric diaphragm type pump two crystals of opposite polarization are sandwiched together so that upon the application of an electrical charge one of the crystals expands radially and the other contracts radially thus causing the structure to bend.

Piezoelectric crystals have substantial strength in compression but relatively small strength in tension. For this reason a piston type pump is capable of operating safely at high pressures although the volume pumped per stroke may be relatively small. In the case of the piezoelectric diaphragm pump the diaphragm can be made of substantial area and thus the pump has ability to pump larger volumes. However, because such a diaphragm pumping action would place the diaphragm under tensile stresses the pressure necessarily is limited.

Accordingly it is an object of the present invention to construct a pump using piezoelectric drive elements in which the construction is such as to maintain the crystals under compression while at the same time actuating a large volume diaphragm arrangement which results in a pump having capability of high volume displacement and at least moderately high pressure capability.

BRIEF DESCRIPTION OF THE INVENTION Two forms of pumps constructed according to the present invention are shown. In each instance a centrally dis- 3,520,641 Patented July 14, 1970 posed piezoelectric pumping element is clamped between a pair of diaphragm members and the piezoelectric elements are so arranged that the diaphragm members can be maintained at ground potential and the excitation voltage applied by way of an electrode between two of the piezoelectric elements. In one form of the pump the diaphragms are of clam shell configuration which are provided with sections of reduced thickness near the outer periphery to facilitate flexing at that point. The outer periphery is clamped together in such a manner "as to place a compressive stress upon the crystal structure. Inlet and outlet valves, of course, are provided. The pumping volume of the clam shell pump is the space between the periphery of the clam shell and the crystal structure. In the second form of pump the diaphragms are in the form of flat plates which are provided with receiving pockets to receive the crystal structure and in addition a central clamping bolt is provided to accomplish axial compression.

For a better understanding of the present invention together with other and further objects thereof, reference is made to the drawing, the following description and the accompanying claims.

DESCRIPTION OF THE DRAWING FIG. 1 is a cross sectional view of a diaphragm pump using clam shell like diaphragms.

FIG. 2 is a cross sectional view of the modified form of the pump of FIG. 1.

Referring now to FIG. 1, piezoelectric crystals 10 and 11 are centrally disposed within a pair of clam shell like diaphragms 14 and 16. Crystals 10 and 11 are secured against lateral movement by retaining rings 18 and 19 on the inner surfaces of diaphragms 14 and 16 respectively. The central portions of diaphragms 14 and 16 are relatively thick and stiff while the outer edges are made thinner as indicated by the arrow at A. Crystals 10 and 11 are separated by a thin electrically conductive plate 12 which is connected to one side of a voltage generator 20 by a wire 21. The other side of voltage generator 20 is grounded as well as connected to the outer shell of diaphragm 16 by a wire 22. An O-ring 24 or other suitable sealing means is located between the edges of diaphragms 14 and 16 as shown. Clamping bolts 26 are provided to secure the outer periphery of the diaphragms. Preferably the dimensions of the crystal structure and the diaphragms will be such that clamping bolts 26 must pull the outer edges of the diaphragms together thus placing the crystals 10 and 11 under a compressive force. An insulating bushing 28 is provided to carry the wire 21 through diaphragm 16. Inlet and outlet pipes 30 and 32 are each provided with check valves as indicated at 34 and 36.

In FIG. 2 like numbers have been used for like parts insofar as possible. In this embodiment the crystal elements and 41 are shown in the form of annular members. Electrical insulation sleeves 42 and 43 are placed on the outside respectively of the annular crystals. A pair of substantially flat diaphragms 46 and 48 are secured together in a manner similar to the clam shell-like diaphragms of FIG. 1 in that clamping bolts 26 or other securing means are provided to clamp the outer periphery in a compressive manner. O-ring 24 is provided as a sealing member. Raised cylindrical sections or pockets 50 and 52 are provided to receive the lower and upper ends of the crystal elements and the insulating sleeves. Hollow central clamping bolts 54 and 56 are provided inside the structure to clamp the same together under compressive stress. The wire 21 from voltage generator 20 is connected to a conductive interface between the crystals 40 and 41.

The face of each diaphragm 46 and 48 is provided at its inner rim with a shallow recess 60, 61. Recesses 60 and 61 are shown in exaggerated form in the drawing for clarity. Recess 61 communicates by a drilled passageway 63 with inlet pipe 30 and recess 60 communicates by way of a drilled passage 62 with outlet pipe 32.

The application of an electrical charge to the conductive layer between piezoelectric crystals by way of wire 21 will cause an axial movement of the piezoelectric elements thus causing movement of the diaphragms. An electrical charge of one polarity will cause the crystals to expand in an axial direction while the application of an opposite polarity will cause the crystals to contract. Application of an alternating current will result in both expansion and contraction and in some instances this may be found to be a desirable mode of operation. It is thus apparent that the application of a cyclical or periodic charge will cause the crystal elements to change dimension thus moving the diaphragms apart and together creating a pumping action within the pumping chamber surrounding the piezoelectric elements. The dash lines of FIG. 1 show the pump in expanded condition and the solid lines in the normal or contracted condition.

In a pump constructed in accordance with FIG. 1, the compression ratio of the pump is relatively low. The piezoelectric crystals are capable of relatively small move ment, for example, a total of about .002 inch. When nonvolatile liquids are being pumped the low compression ratio is of little importance. If volatile liquids or gases are to be pumped the compression ratio assumes much greater importance and the pump of FIG. 1 might well prove unsatisfactory. This aspect of the pumping condition is overcome by the structure of FIG. 2. As mentioned earlier the recesses 60 and 61 are very shallow. The depth required being only enough to insure that there will not be complete closure or contacting of the opposing faces in order that there be free access and exit by way of the inlet and outlet passages 63 and 62 at all times. With recesses 60 and 61 made very shallow, then the compression ratio of the pump becomes very high and volatile fluids and even gases can be handled by the pump. It necessarily follows that inlet and outlet valves 34 and 36 will be placed as close as possible to the pumping chamber in order to keep dead space to a minimum. It would, of course, be possible to incorporate the inlet and outlet valves in the housing of the pump thereby further reducing the aforementioned dead space.

I claim:

1. A diaphragm pump comprising a pair of diaphragm members, peripheral clamping means for clamping the periphery of the diaphragms together to define a pump ing chamber, piezoelectric actuating means centrally disposed between the said diaphragms to partially fill the said pumping chamber, electrical energizing means for energizing said piezoelectric actuating means which upon energization creates relative movement of said diaphragm members, and inlet and outlet valve means in communication with the said pumping chamber.

2. A pump according to claim 1 including retaining means for securing said actuating means from lateral movement.

3. A pump according to claim 1 or 2 in which the said diaphragms are of claimshell-like configuration having a generally convex outer surface and a generally concave inner surface.

4. A pump according to claim 1 in which the said diaphragms are substantially fiat and the said actuating means is received in opposing pockets in each of said diaphragms.

5. A pump according to claim 4 in which the said actuating means is annular in form and there is further provided a hollow clamping means in the center of said actuating means for providing a clamping force at the central portion of said diaphragms and of said pump.

6. A pump according to claim 4 or 5 in which there is further provided a shallow recess at the inner rim of at least one of said diaphragms, said recess being in direct communication with at least one of said inlet and outlet valve means.

7. A pump according to claim 1 or 4 in which the said actuating means includes at least a pair of oppositely polarized piezoelectric crystal elements positioned on either side of a conductive surface such that surfaces of like polarity contact said surface and said surface is connected to a voltage generator for energizing said actuating means.

References Cited UNITED STATES PATENTS 1,400,578 12/1921 Sweet 103-148 2,019,160 10/1935 Semsch 103148 2,317,166 4/1943 Abrams 103152 2,664,826 1/1954 Dufiing 103152 2,842,067 7/1958 Stevens 103-152 3,150,592 9/1964 Stec 103-1 3,361,067 1/1968 Anderson l031 WILLIAM L. FREEH, Primary Examiner US. Cl. X.R. 103148; 123-32 

